A valve system formed as an intake or exhaust system, hereinafter designated as valve system, for controlling the charge exchange in an internal combustion engine comprises in addition to the intake valves also the exhaust valves. The valve system determines when and how much fresh gas is introduced into the combustion chamber, and it controls when the combusted gas is expelled. On all system components, and in particular on the valve seat ring and the valve seat associated with the valve seat ring, high material requirements are placed. Accordingly, these components must have high fatigue strength and must be mechanically and thermally highly resistant and must have a high wear resistance. For this purpose, depending on the requirements specification, different materials can be combined with each other and the respective positive material properties can be used to optimally support the individual components of a valve system. Thus, for reducing wear and increasing the service life, the valve systems can be further optimized in a requirement-specific manner, for example by hardening the valve seat or build-up welding with a special hard-facing alloy by means of which the valve seat is hard-faced. In order to improve the wear behaviour of the valve stem, said valve stem is often nitrated or chromed.
From U.S. Pat. No. 6,318,327 B1, a valve system for an internal combustion engine is known which comprises a valve seat and a valve element associated with said valve seat, wherein the valve seat has a base element comprising a matrix of iron-based sinter alloy and dispersed therein a powder from an intermetallic compound of the Si—Cr—Mo—Co group, said powder having a hardness of 600 to 1000 HV and an average particle diameter of 20 to 70 μm and being contained in the matrix in an amount of from 10 to 50 percent by mass based on the total mass of the base element. The valve system is characterized in that the valve element has a base element comprising a matrix of martensitic steel and a nitriding diffusion layer formed on a valve surface of the base element, the nitriding diffusion layer having a hardness of more than 500 HV and a thickness of more than 20 μm.
With the nitriding diffusion layer on the valve element in the known valve system, an improved wear and abrasion resistance is achieved; however, temporary adhesive bonding or, respectively, punctual welding of valve seat and valve seat ring cannot be avoided.